Brief Description of Ear Canal Anatomy and Physiology
The ear canal 10 (FIGS. 1 & 2) is generally narrow and tortuous and is approximately 26 millimeters (mm) long from the canal aperture 11 to the tympanic membrane 15 (eardrum). The lateral-part 12 is referred to as the cartilaginous canal due to the underlying cartilaginous tissue 19. The cartilaginous region 12 of the ear canal 10 deforms in shape and moves in response to the mandibular (jaw) motions, which occur during talking, yawning, eating and also when sleeping over the ear. Hair and earwax (cerumen) are primarily present in this cartilaginous region 12. The medial part, proximal to the tympanic membrane 15, is rigid and referred to as the bony region 13 due to the underlying bone tissue 7. The skin in the bony region is very thin relative to the skin in the cartilaginous region and is far more sensitive to touch or pressure. The bony region has little tolerance to touch and pressure. A characteristic bend roughly occurring at the bony-cartilaginous junction 8 separates the cartilaginous region 12 and the bony region 13. The dimensions and contours of the ear canal vary significantly among individuals. There is a characteristic first and second bends generally occurring at the aperture area 11 and junction area 8, respectively. Leading into the ear canal is the concha 5 which aids in the collection of sound into the ear canal.
A cross-sectional view of the typical ear canal (not shown but described in details in cited references) reveals generally oval shape with a long diameter in the vertical axis and a short diameter in the horizontal axis. Canal dimensions vary significantly along the ear canal and among individuals. FIG. 2 shows an alternate view of the ear canal 10 (top-down) indicting the narrowness of the contoured ear canal and the challenge of placing and navigating a receiver assembly 41 in the bony region. Placement of a hearing device entirely in the bony region is problematic for most individuals even with the smallest miniature electroacoustic components available. Furthermore, access and manipulation of a miniature canal device becomes prohibitive when placed too deeply in the bony region. However, it is desirable to deliver sound in the bony region to achieve electroacoustic advantages including reduction of the acoustic occlusion effect, improved energy efficiency, reduced distortion, reduced receiver vibrations, and improved high frequency response. Unfortunately, placing a hearing device in the bony region is difficult due to space and canal contour constraints.
Physiological debris is primarily present in the cartilaginous region 12 of the ear canal, and includes cerumen (earwax), sweat, and oils produced by the various glands underneath the skin in the cartilaginous region. Debris in the ear canal is a major cause of damage to canal hearing devices resulting in frequent and costly repairs. Canal hearing devices on the market are mostly custom made with few exceptions. Generic canal devices currently have limited market acceptance due to poor fit, limited performance and reliability.
Several types of hearing losses affect millions of individuals. Hearing loss naturally occurs as we age beginning at higher frequencies (above 4000 Hz) and increasingly spreads to lower frequencies with age. It is estimated that over 30 million Americans suffer from hearing loss and the vast majority remain untreated due to the high cost of inconspicuous hearing devices and hassles of ownership.
The Limitations of Conventional Canal Hearing Devices.
The limitation of current canal hearing devices is well described in U.S. Pat. No. 6,473,513 and U.S. Pat. No. 6,137,889 incorporated herein by reference. These limitations include the well know occlusion effect (speaking into a barrel effect), dexterity limitation for placing a device deep in the ear canal, device size for fitting a miniature device into ear canals, particularly in small and contoured ones. A major limitation is the propensity of canal hearing aids (referring to both ITC and CIC types throughout the application) to feedback (whistle) when set at moderate volume settings or higher.
Current canal devices are mostly custom made requiring an impression of the ear canal to fabricate a custom shell and place electronic and electroacoustic components within. This process is notoriously inefficient leading to high cost, high rates of remake and return-for-credit. Because of their placement, primarily entirely in the cartilaginous region, custom canal devices are highly prone to contamination from ear canal debris. However, placement in the cartilaginous region as compared to the bony region has the distinct advantage of improved access and comfort of wear since the tissue there is more tolerant to frequent touch and pressure. This bony region is prone to damage and irritation when touched by any rigid part or when subjected to pressure.
It is a principal objective of the present invention to provide a canal hearing device that delivers sound within proximity to the eardrum while providing easy access to the hearing impaired user.
Another objective is to provide a cost effective generic design that can fit the majority of individuals without resorting to custom manufacturing.
A further objective of the invention is to provide acoustic sealing in the bony region for providing acoustic occlusion relief without placing a rigid structure therein.
A major objectives is to provide a new hearing aid form-factor that is inconspicuous to alleviate the stigma of hearing aid wear.
Another objective is to provide a more reliable miniature hearing aid design with predictable function and operation.
And finally, a major objective is to provide a miniature hearing aid design that is easy to maintain and does not require repair.